The government has changed its mind over the type of fighter planes it is ordering for the Royal Navy's new aircraft carrier.
Defence Secretary Philip Hammond said the F35-C had hit development problems and it would be cheaper in the long term to order F35-B jump jets, as originally planned by Labour.
The cost of the U-turn is likely to be about £100m, he told BBC News.
Labour said it was an "omnishambles" which risked "international ridicule".
Mr Hammond said delays to the F-35C Joint Strike Fighter programme, a multinational venture led by American company Lockheed Martin, meant they would have not been operational until 2023 - three years later than planned.
"When the facts change, the responsible thing to do is to examine the decision made and be willing to change, however inconvenient that may be," said Mr Hammond.
'Facts have changed'
As part of its SDSR defence spending review in 2010, the government decided to "mothball" one of the two aircraft carriers, HMS Prince of Wales and HMS Queen Elizabeth, ordered by Labour.
Abandoning the plan to fit the "catapults and traps" needed by the F35-C to one of the carriers while mothballing the other, opened up the possibility that both could eventually become operational, said Mr Hammond.
"The 2010 SDSR decision on carriers was right at the time, but the facts have changed and therefore so too must our approach. This government will not blindly pursue projects and ignore cost growth and delays," said the defence secretary.
"Carrier strike with 'cats and traps' using the carrier variant jet no longer represents the best way of delivering carrier strike and I am not prepared to tolerate a three-year further delay to reintroducing our carrier strike capability.
"This announcement means we remain on course to deliver carrier strike in 2020 as a key part of our Future Force 2020."
The estimated cost of fitting the "cats and traps" system to HMS Prince of Wales had risen from £950m to £2bn "with no guarantee that it will not rise further".
But, he revealed, the government had spent between £40m and £50m on design and assessment work and there would also be penalty costs associated with scrapping the F-35C deal.
He told MPs the eventual cost of the U-turn would be "nowhere near" the £250m claimed by Labour and warned "fiscal incontinence" over defence procurement would undermine "the support we should offer our armed forces".
When pressed about the cost of the rethink on BBC Radio 4's The World at One he said it would be in the region of £100m. Labour has called on Mr Hammond to publish the full costs.
Unveiling the decision to "mothball" one of the carriers and order the F35-C in October 2010, as part of the government's defence review, David Cameron attacked Labour's "appalling legacy" on defence procurement and said decisions were "now being made in the right way and for the right reasons".
Shadow defence secretary Jim Murphy said Mr Cameron should now apologise for the government's "incompetence", saying that the prime minister had ignored warnings from the Public Accounts Committee and the National Audit Office about the "high risk and high cost" of opting for the F-35C.
"It is as incoherent as it is ludicrous," he said. "The prime minister's decisions have cost British time, British money, British talent and British prestige.
"Describing this government's defence strategy as an omnishambles would be a compliment.
"The previous Labour government got it right and this government's policy has unravelled."
He said the government should never have scrapped its Harrier jump jets, which he said had been "sold off to America for a fraction of their value" - a decision he said risked "international ridicule".
Labour peer and former security minister Admiral West described the U-turn as a "shambles".
"It is extraordinary, it does smack of total incompetence. I'm just utterly amazed," he told the BBC's Daily Politics.
Lord Stirrup, who was head of the armed forces when the 2010 decision was made, said the government had made a "perfectly rational decision" to backtrack after discovering the "true nature of the costs and the risks that are involved".
But former Labour defence secretary Bob Ainsworth said the 2010 decision "was taken in the face of clear advice" and the facts had not changed in the way Mr Hammond claimed.
"I reviewed this decision, taken by my predecessor. The fundamental facts were there at the time and have not changed.
"We have been in an extremely expensive cul-de-sac for the last 18 months as a result of a shambles of an SDSR and I can only congratulate you for bringing some sanity to it," he told Mr Hammond in the Commons.
Mr Hammond insisted the risks associated with the F35-B were "dramatically different now" to what they were in 2010 when there was a possibility it would be cancelled due to technical problems.
F-35B stealth jump jet
F-35B STOVLShort Take Off Vertical Landing
Cost per aircraft: £65.5m*
Combat range: 1,667km (900nm)
Selected: Trials by 2018
F-35C Carrier VariantHook wire landing system
Cost per aircraft: £59.9m*
Extra cost to adapt carrier: £2bn
Combat range: 2,200km (1,200nm)
Rejected: Due to carrier conversion costs
The Royal United Services Institute said the vertical take-off and landing F35-B version is likely to cost more per plane and will have a shorter range and payload capacity than the conventional take-off and landing F35-C. Royal Navy pilots and ground staff will also have to be retrained in the use of jump jets.
The U-turn also means French aircraft will not be able to land on British carriers but Mr Hammond insisted this would not get in the way of joint carrier operations. It will also be compatible with the Italian Navy and the US Marine Corps, the government has said.